Fuel injectors with atomizer nozzles have between 4 and 7 small holes in the nozzle, approximately 0.2 mm in diameter. In use, these holes are frequently reduced in size, or blocked entirely, causing an imbalance in the spray pattern of atomized fuel into the cylinder and a consequent imbalance in the air-fuel ratio, resulting in incomplete combustion.
This incomplete combustion manifests itself in power loss and black smoke emission from the exhaust. Continued operation of an engine under such conditions results in irrepairable damage to the injector, the piston and the cylinder head, in that sequence.
A faulty injector still in the engine can only be detected when it has failed completely. The engine is run at idle and each injector fuel supply connection is eased, in turn, until fuel leaks out. Under this condition, the injector will fail to operate. If, when the nut is eased, the idle speed is markedly affected then that injector is operating properly. Conversely, easing the nut on a faulty injector has no affect on the idle speed. This known method of testing fuel injectors is a time consuming inefficient method.
The applicant knows of no means of reliably detecting faulty injectors before failure thereof. The most widely practiced method of dealing with the problem is to remove and replace all injectors at specified service intervals. Another common detection method for a faulty injector is the "black smoke" test (a vehicle expelling 10 seconds or more of black smoke detected against the sky line). A loss of power under load is also an indication of fuel injection problems.